


Proper teeth for a proper bite

by themunak



Category: Katekyou Hitman Reborn!
Genre: Alternate Universe, Alternate Universe - Shapeshifters, Animal Transformation, Gen, Supernatural Elements
Language: English
Status: In-Progress
Published: 2014-11-17
Updated: 2014-12-01
Packaged: 2018-02-25 18:37:26
Rating: Mature
Warnings: Graphic Depictions Of Violence
Chapters: 3
Words: 4,570
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/2632106
Author URL: https://archiveofourown.org/users/themunak/pseuds/themunak
Summary: <blockquote class="userstuff">
              <p>Hibari has always been his strongest Guardian, not to mention the most terrifying, but this battle takes him to whole new heights of 'monstrous'.</p><p>There's a reason Hibari is, well, <i>Hibari</i>, and Tsuna thinks he's finally found out why.</p>
            </blockquote>





	1. Chapter 1

**Author's Note:**

> Where did the inspiration for this come from? Maybe SMT, or Wolf's Rain, or Yozakura Quartet, or even specific works by SkyGem and Bleach-ed-Na-tsu over at ff.net. I have no idea exactly, but I'm pleased with what's come of it.

There's a new yakuza clan moving into town to make it its territory-- or at least, there used to be. The moment the rumor mill had reached the ears of the young Vongola Don-to-be, his Guardians had immediately taken action, the Cloud with even more fervor then the rest.

Hibari is even more animal-like than usual, baring his teeth in such a frightening grimace that Tsuna would like nothing more than to go home and leave it to his Guardians, Reborn's punishments be damned. That crazy light in Hibari's eyes is something no one should ever be witness to. _Ever._ Least of all his own boss, because how in the world will Tsuna be able to face him in the morning without remembering how effectively he destroyed the yakuza troops.

Hibari has always been his strongest Guardian, not to mention the most terrifying, but this battle takes him to whole new heights of 'monstrous'.

When Hibari manages to catch up with the boss in his room, Tsuna in tow to bargain for the poor man's life if needed, he discovers something that he'll never be able to forget, no matter what he does, or how long it takes.

The yakuza growls, an actual, animal's growl. It sounds like a dog's growl, like the giant mastiff that lives a few blocks over from Tsuna's house and likes to bark at him whenever he passes by on his way to Yamamoto's place. And Hibari for his part _answers_ with his own.

It's impressive. That's one word for it. Low and so strong that Tsuna can feel it reverberate in his chest, and he's pretty sure everyone else had heard it, no matter where they are in the compound. It doesn't have the same quality as Natsu's when he's in battle, or even Bester's, but Tsuna is pretty sure that it's something out of one ofthose animal documentaries that one of his old science teachers used to bring to school.

But Hibari doesn't stop at just growling. He takes onestep forward, towards the now cowed yakuza, and _shifts_. Actually shifts, his body becoming a little more muscular, almost like Ryohei's, clothes stretching around the new muscle he'd just grown. His ears morph to gain a more pointed look, and Tsuna cant help but think that they make Hibari look even more feral. But it's his face that grabs Tsuna's attention so thoroughly that he doesn't know whether to run away screaming or continue to look on in awe. Instead of the small, blunt nose and high cheekbones, Hibari now sports a prominent, sloping snout, face pushed forwards just a little more, giving him a positively inhuman look, thinned lips drawing back to show off a full set of sharp, _deadly_ teeth-- no, _fangs_ , thick and curved and definitely made for sinking into meat.

"You may have fangs, but you don't know how to use them." Even his voice has changed-- or is that because his face has changed that he sounds so much more gruff now? "For trespassing into my territory and pretending to be a predator, I will _bite you to death._ "

If there's one thing Tsuna has never seen Hibari do, it's literally bite someone to death, but bite he does. He opens that mouth wide, wider than he's ever seen any human do, and sinks them into the poor yakuza's forearm, abandoning his tonfa in favor of using his teeth. Immediately the bleeding starts, and only gets worse when the oyabun starts yanking his arms this way and that, in a futile attempt to dislodge Tsuna's Cloud Guardian.

Right then and there, Tsuna thinks that it's time to step in, because he doesn't want this kind of death on his hands, or on his Guardian's. Because he feels that Hibari has been hiding this side of himself for a reason, and he cant let this situation go any further, and if he literally bites this man dead, he's sure it will get problematic. Because everyone who knows about the criminal underworld will know that this is a Vongola operation even if Tsuna doesn't want it to be, and if word gets out that the boss had been murdered by some kind of wild animal, all eyes will be on the Vongola and make things just a little more uncomfortable for all of them.

So he steps forward, the Dying Will Flame that has been flickering to a small spark due to his doubts flaring up once again on his forehead, and places a hand gingerly on Hibari's shoulder. He doesn't even flinch when Hibari releases the man's arm to whirl around to face him, face bloodied and teeth still bared-- he only meets Hibari's eyes and holds his gaze.

"We're done here. We're only here to drive them out of town and send a message, not kill. They wont be bothering Namimori anymore after this."

If the frantic, panicky blubbering and begging the oyabun is doing, then they'll definitely be packing up and leaving immediately after the Vongola leave the compound.

Hibari stares at him for what feels like an eternity, before blinking slowly and changing once again before his very eyes. Now that he's so close, Tsuna can practically hear his bones creaking as his body rearranges itself to the features that Tsuna is more familiar with, and he has to wonder what else changes in his body other than the obvious.

At the same time, hearing those sounds makes him just a little sick, dispelling his Dying Will, because _what if it hurts Hibari to change like that?_ He doesn't look like he's in pain, but then again, Hibari never shows that kind of expression, and that fact only serves to increase his worry over his Guardian. But there's not much he can do when Hibari just refuses to talk, and he cant force him to, so all Tsuna does right now is lift an arm and wipe at Hibari's mouth with his long sleeve, taking extra care not to catch his skin with his rings or the chain connecting them. Hibari allows it for a few seconds-- practically a long time when it's _Hibari_ \-- and then pushes Tsuna's hand away so he can gather his tonfa and stalk out of the room.

"Don't do something unnecessary again, little animal."

There's a reason Hibari is, well, _Hibari_ , and Tsuna thinks he's finally found out why.


	2. Chapter 2

Tsuna has not breathed a word of Hibari's transformation to anyone, not even Reborn, though he's pretty sure his tutor can tell that he's hiding something-- the sadist always seems to know everything when it comes to Tsuna. But this is about respecting Hibari's privacy, and Tsuna's taking it with him to the grave, Reborn be damned.

Still he cant help but be curious, and he wants to ask Hibari about it. And if he can help in any way. He knows his Cloud is prideful, and absolutely hates being questioned about his private life (or about anything in general), but... in the same way that it's Hibari's nature to be violent, bloodthirsty, and tight-lipped about his personal life, it's in Tsuna's nature to want to make sure that all of his friends are all right.

And he's keeping that particular thought in mind as he makes his way through the hallways towards the Reception Room during lunch time, two bento in tow in case his Guardian hasn't eaten yet. Or at least try to. He might just royally piss Hibari off and get thrown out the window. Or chased around campus by an army of Rolls in Needle Sphere Form. Or bitten to death. Or _literally_ bitten.

None of those thoughts fill him with any hope!

For what seems like an eternity of staring at the door and debating whether he should just turn back and have lunch with his other Guardians, the decision is made for him when the door opens to reveal Hibari, who is not at all surprised to see him there.

In fact, he... kind of looks annoyed. Something tells him that Hibari knows he's been hanging out just outside his door, and has gotten impatient just waiting for him to either leave or open it.

Tsuna might not be making it out of this meeting unscathed.

"Stop loitering, or I will bite you to death."

"Eeeek!! I'm sorry! M-may I come in?"

"What do you want, Sawada Tsunayoshi?"

"Er, um, ah... I was hoping we could t-talk and..." Finding that words just fail him right now, he holds up the furoshiki-wrapped bento boxes to Hibari's eye level, hoping against hope that he wont get a tonfa to the face just for that one small gesture.

"I told you not to do something unnecessary."

Tsuna notices Hibari's hand twitching, the one with the Bracelet, and he really has to think fast now. "I-it's not unnecessary! It's _lunchtime_ and eating is what people do right now!"

He cant believe he just said that.

What he cant believe more is that _it actually works_ (or is he being so dumb that Hibari feels compelled to just humor him?), because Hibari steps aside to let him in. A little. Tsuna needs to squeeze between his maybe-not-human Guardian and the doorway to get into the room, leaving him brushing against Hibari's body as he goes.

Weird though-- Tsuna almost expects him to run warmer (or maybe colder?) than humans, but touching him, even just briefly and through a layer of clothing, feels like touching anyone else.

Pushing that thought aside, he unwraps the furoshiki, leaves one box and set of utensils on Hibari's very clean desk and sits down with the other on the couch. He doesn't open it yet, because he's too busy warily staring at his Guardian as he sits down on that big chair, drags the box towards him, and inspects its contents with a critical eye. But he does twitch when that stare goes to him and Tsuna finds himself comparing it to a predator sizing up its prey-- _no, bad brain, stop that!_

"if you want to ask, just ask, and I'll decide whether to bite you or not later."

Tsuna thinks that he'll be bitten to death anyway, so he might as well do something to deserve getting bitten. "Well, Hibari-san, you see... That thing with the yakuza. You, uh, _changed._ "

Hibari doesn't look surprised at that either. In fact, he looks even more annoyed and... Resigned? Is that even possible for him?

For a while, Hibari doesn't reply, and instead takes up his chopsticks to pick at his meal (looking for the meat, Tsuna bets), leaving Tsuna wilting at the stifling, extremely awkward quiet, because what exactly is going on in that head of his? The silence stretches on for several minutes, Tsuna getting more fidgety as it drags on. He's about to jump up, stammer his apologies and rush out of the room to find some solace in Gokudera and Yamamoto, but then Hibari finally, _finally_ speaks again.

"I'll tell you if you fight me, and fight me seriously."

... Oh, _no_.

And the worst part is that Tsuna doesn't get a chance to say no, because the look on Hibari's face tells him that he'll fight no matter what he says. And if he says no... nope, he doesn't want to think about what will happen if he refuses.

The thing is, he never promised to tell him the _whole thing_ all at once, and Tsuna will forever kick himself over that oversight because Hibari has successfully manipulated him into fighting him a whole lot in order to hear the story in installments. So after several painful, back-breaking, soul-crushing sessions over the course of a month, he's finally gotten the whole story, and what a story it is.

He's a wolf.

Tsuna didn't even know that Japan _has_ wolves. Or had. It's still all very confusing to him, but apparently the Japanese wolf, the okami or yamainu, is supposed to be extinct, and has been said to be extinct for over a century. But there's a good reason for this, because according to Hibari, the wolves foresaw their end several years before humans themselves even noticed and decided they needed to do something to stay alive and keep their lines going-- they learned how to disguise themselves as humans and live among them. Hiding in plain sight, Hibari calls it.

Tsuna's not really sure about how _that_ came about, something about wolves being very close to the supernatural and the kami and stuff, but it does explain the shapeshifting he'd been witness to.

The Hibari family-- well, _pack_ , really-- took up birds as their symbol in order to 'hide their true nature' and settled in Namimori. They made it their territory, and like any proper pack, they had the entire town under their thumb, driving away other packs, and tolerating the humans and other supernatural creatures within its boundaries as long as they obeyed the rules. It definitely explains Hibari's fierce protectiveness towards the town.

Hibari had also mentioned that he's not entirely wolf stock either-- because there's so few of them, in-breeding (oh, urgh) seemed inevitable, but because they had a natural aversion to that, the wolves had to look for an alternative, so his ancestors ignored their pureblood pride and made use of other species whenever necessary. One of them was (is? Hibari used 'is' to describe her, which is probably a clue that she may still be around somewhere) a big black dog creature that came into the country with traders after the ports opened. He'd also mentioned another relative from another country who's neither wolf nor dog and is part human to boot, but he threw Roll at Tsuna when he tried to ask more about _that_.

So he's more of a wolf-dog-maybe-something-else than a pure okami, with some human blood mixed within. Human enough to use Dying Will Flames, at the very least, because that kind of thing seems limited to humans.

But even with that overly-long, and ridiculously complicated background, it explains _so much_ about his Guardian. His personality, his mannerisms, his _thing_ for biting... Almost everything. The reason why no one has ever been able to understand him is because he's more supernatural being than human.

Does _Tsuna_ understand him a little more now that he knows? Maybe yes, maybe no. He still has no idea what goes on in Hibari's head, but now he knows that he should think out of the box a little more when it comes to his Guardian.

And make sure not to ask him any more about his personal life, because he's probably not going to survive the price he needs to pay to get more out of him. _Ow._


	3. Chapter 3

**Notes for the Chapter:**

> Warning: Body horror alert! If you've read Animorphs, you'll know what to expect, because I took some cues from KA Applegate. ... And enjoyed writing it a _little_ too much.
> 
> This fic was supposed to only have three chapters, but this one got so long that I decided to just cut it into two and end this chapter in an ambiguous way.

Unfortunately, secrets tend not to stay secret for very long, and even if Tsuna kept his word and stayed mum about Hibari and his otherness, it'd still come out because sometimes Hibari just has _no sense of control._

He probably should have seen it coming. Scratch that, he _has_ , thanks to his Hyper Intuition acting up earlier that day when he passed Hibari at school, but like an utter moron, he ignored it in favor of surviving Reborn's daily Spartan training.

Two of Mukuro's gang, namely Ken and Chikusa, and sometimes accompanied by Chrome, come into town regularly for supplies. It just so happens that during one of their supply runs, they have the misfortune of running into the last person they should ever come across. But because the universe hates Tsuna, Hibari's patrol coincides with that one supply run, and one thing leads to another. Which then leads to Chrome calling Tsuna on his phone for help (he'd gotten her that cellphone for her birthday so she can always keep in touch with the people she cares about, but he's not expecting _this_ to be her first-ever phone call to him), and before he manages to properly process things, he's run across town with Gokudera and Yamamoto in tow and and is now watching his Cloud Guardian and Ken going at it like wild dogs in the back alleys.

Scratch that, they're going at it _as dogs_.

Ken obviously has the Wolf Channel on, intending to take Hibari down with speed instead of strength, but nothing really prepares anyone for Hibari's true form. Especially when he very clearly sees Ken's methods as a personal challenge.

"You're pretending at being a real wolf again, little dog. This time, I'll bite you until you stop."

Tsuna has already seen him change just a bit, but it's nothing compared to a full one. There are no bright lights to censor things, or an instant change like in the movies, or even the sudden sprouting of ears and a tail like in cartoons. Not even a puff of smoke like in ninja manga. Watching Hibari change is like watching a horror movie. One with a scarily competent animation and design team that worked really hard to get every single detail right.

That's not a good thing if you're seeing it in person.

Hibari steps out of his shoes, drops his tonfa, removes the Bracelet, and strips off the jacket with the ever-present armband, and for good reason, because his arms and legs are the first to change now and unlike on TV or in manga, clothes are apparently _not safe_ from real world transformations.

Tsuna can see his legs changing shape, knees bending at awkward angles, new joints appearing where they shouldn't be and his pants legs and socks are ripping because they just aren't made for something other than human legs, leaving him partially bare. And now there's no way to ignore all the changes going under his skin-- he's no good in anatomy, but he can practically see moving bulges where the bones are changing shape (with _crunching_ sounds that makes Tsuna feel sick), with the muscles shifting to accommodate them. Human legs just don't have that same kind of curve to them, and his feet... Hibari is definitely standing on his toes.

No, he should start calling them paws. But because the rest of him isn't made for standing on that kind of structure, he falls forward-- no, Hibari doesn't _fall._ He deliberately drops down onto his hands. Hands that are now getting thicker but less broad than a human palm, with fingers that are shrinking into themselves before reforming into toes, thumb becoming a bump with a dark brown claw that Tsuna can barely see at this angle. But this angle gives him a better view of Hibari's _spine_ that's rippling, getting longer, until he can see something poking out from his lower back.

Something that starts out short and then grows out to become longer than Tsuna's forearm, almost whiplike with how thin it is, but it's definitely not limp. It stays up in the air, a thing raised high with a slight curve at the end jutting from Hibari's back, and only then does he realize that it's his tail. A tail that doesn't look like a wolf's tail because Hibari's fur hasn't grown in yet.

Once again, it's his face that gets Tsuna's attention, pushing outward and not stopping until it forms a blocky snot and a low forehead. His nose has turned black, his ears have become more rounded with pointed tips and have rolled up higher on his head, and his eyes... well. Even if they've shifted in position and shape, and are now heavily lined with black like he's wearing eyeliner, they're still very much the pale grey that Tsuna is used to.

Meanwhile, his shoulders rearrange themselves, thrusting forward and making his back seem more broad, and his arms shift too, supporting his upper body better because... Because he's definitely gaining more muscle there. There and elsewhere, with the fur finally growing in, as black as the hair on his head, greyish around the face and muzzle, underbelly and the insides of his big ears, but more layered and shaggy-looking, standing on end to make him look even bigger than usual, especially around his longer neck.

The transformation is complete, the last parts of Hibari's human self disappearing to give way to the okami, the last scraps of what had been his uniform falling away from his body, and Tsuna feels faint. It feels like it's been forever since he's been watching Hibari change, but his intuition tells him that it couldn't have been more than a minute.

All that, crammed into a minute, or less. That's why Tsuna feels overwhelmed.

And, he thinks, so does everyone else in attendance. The cigarette Gokudera's lit up for his bombs is on the ground at his feet, burning itself into a stub because his fingers have gone slack with shock. Yamamoto isn't smiling, the lines of his eyes hard, a hand on his Necklace. Chrome has her spear out and looks ready to drive that pointed end into some unfortunate soul. Chikusa has his yo-yos in his hands, knuckles turning white around them with how tightly he's probably holding them. And Ken... Ken has his teeth bared and his shoulders hunched in a defensive position, growling.

In reply, Hibari-the-gigantic-wolf steps forward, keeping eye contact, slowly drawing back his lips to reveal a full set of really impressive fangs. And then suddenly Hibari is in front of Ken, that mouth full of giant teeth wide open and aiming to close around his neck.

Ken's lucky that his Channel's reflexes allows him to move back quickly so all Hibari's jaws close in on is thin air, but it drives home the fact that Tsuna needs to do something. Chrome didn't call him in to be a spectator after all.

Tsuna pulls on his mittens and draws up his Hyper Dying Will without the need for a bullet or pills, the change now as easy as breathing. "Gokudera, get Chikusa out of the way. Yamamoto, cover Chrome. Whatever you do, do _not_ make eye contact with Hibari, do not try and fight him at all, and do not run."

Both of his Guardians snap into action at the sound of his voice, and he knows they wont let anything stop them from carrying out their orders.

And so he turns to Hibari and Ken. His Hyper Intuition has never encountered a giant wolf before, but Tsuna still notices how thick the fur around Hibari's neck is-- gigantic and long, perfect for grabbing and holding his entire body in one place without hurting him too badly. It would also get him an easy to make eye contact with Hibari-- despite his warning to his Guardians, it worked so well last time, so it may work again now.

No, he's _sure_ that it will work again, and only with him.

He leaps towards Hibari, but misses when the wolf makes another lunch at Ken and gets a large back paw in the face for his trouble. But even with his miss, he finds himself in a much better position than before-- he's much closer to Hibari, giving him a much bigger chance of success. So he jumps again, the dying will fueling him.

Tsuna shoves Ken away with one hand on his chest, while the other deflects Hibari's jaws, and he's ever thankful that his Vongola Gear is not just for show, but actually shields his body-- or at least the parts they cover. If he didn't have that guard, he'd probably have broken that arm. With Ken finally out of the way, he steps forward and digs both hands into that thick ruff of fur around the wolf's neck. Hibari protests this kind of handling by snapping his jaws and throwing his body weight around in an attempt to thrash, but Tsuna digs his heels into the ground and forces small bursts of soft Sky Flames out of his gauntlets to stabilize himself, and he's absolutely not willing to let Hibari go until the situation has calmed down. But _goddamn_ if Hibari isn't much stronger in this form. He's sparred with him several times before, and this wolf version of his Cloud Guardian has more power in his muscles than the human one, so Tsuna knows he needs to make this quick.

He threads his fingers into black fur the way he'd comb through his own hair, carefully, as to not harm Hibari or even pull out a lot of individual hairs, but still make sure that Hibari cant pull away without great effort or doing harm to himself.

Not that he thinks Hibari will hesitate to do great bodily injury to himself-- because he _knows_ Hibari will if he believes it's the only way to allow him to bite someone he has a problem with to death.

With everything now relatively settled, nobody speaks, the only sounds in the dirty back alley being Gokudera's wordless exclamations of annoyance at Chikusa, and Ken huffing and growling back at him, and Hibari breathing loudly through his mouth. Their faces are so close that Tsuna and he are sharing breaths, that there are only a couple of inches between their noses.

Staring into the eyes of a wolf is very different from staring into the eyes of a human, or even a dog, Tsuna decides. There's undoubtedly intelligence and self-awareness in Hibari's eyes, so he's very obviously in control of himself and knows exactly what he's doing (trying to bite someone's head off with a single snap of his jaws), but at the same time…

It's like looking into a well. It's deep, and the further you look into it, it seems to get darker and darker, so you're not sure whether you're looking at the water or the stone wall the further down you check. And the longer you stare… the more you feel that there's no end to it, and at the same time, there's something staring back at you at the bottom of it.

It makes cold sweat break out on Tsuna's back and his Dying Will Flame flicker for just a bit, but he holds on, and bares his teeth at Hibari to show that he's serious, because his Intuition tells him that it's the right thing to do in this situation.

And finally, _finally_ , after what seems like forever, those steel grey eyes blink slowly. Once, twice, and a third time before Hibari grins, upper lip curling up to bare his utterly terrifying teeth (and Tsuna is glad for his Dying Will tamping down on his fear, otherwise he would have pissed himself). He looks like he's grimacing or sending a warning, really, but Tsuna just knows that this is the wolfish version of a smirk, the indescribable one that he sends to Tsuna when he's in his human skin, and only to Tsuna. The one that would be accompanied by a 'wao'. And when he shakes himself again, Tsuna lets him go and steps away.

Hibari leaves his things behind when he lopes off through the dirty street, and Tsuna just _knows_ he did that on purpose, because he knows that Tsuna wont leave them behind, thus giving them a legitimate reason to meet up again. Nevertheless, Tsuna gathers what little the transformation's left intact in his arms.

But when he leaves Hyper Dying Will Mode, he utters a weak, breathy cry of utter terror and sinks to his knees, legs suddenly feeling like jelly.


End file.
